InStr Function

Posted on 2007-04-07
Last Modified: 2008-02-01
Could you help using these two functions in .net way?

InStr Function
InStrRev Function
Question by:VBdotnet2005
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Assisted Solution

Mamtha1982 earned 100 total points
Comment Utility
use IndexOf and LastIndexOf functions for string objects.

Dim s As String = "Wel Come"
Dim i As Integer

i=s.IndexOf("e") 'stores 1 into i
i=s.IndexOf("C") 'stored 4 into i
i=s.IndexOf("xx") 'stored -1 into i, because xx is not found

LastIndexOf function will return the index position, but it will search from end.

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Expert Comment

by:Mike Tomlinson
Comment Utility
If you are converting legacy code, don't forget that most VB6 functions are "one based" while .Net functions are "zero based".
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Accepted Solution

VBRocks earned 150 total points
Comment Utility
Mamtha1982 is right, and all credit to him, the Instr and InStrRev functions are still supported in .NET, but they are not the official way to handle strings.  If it's ok, I would just like to elaborate a little for your better understanding.

The IndexOf and LastIndexOf functions are available for every string in .NET.  So, for example:
Dim i as Integer

'Use the "IndexOf" method with a regular string.
i = "My String".IndexOf("String")

'Use the "IndexOf" method with a string variable.
Dim str as String = "This is another string"
i = str.IndexOf("string")

'Use the "IndexOf" method with a TextBox, because the "Text" property is a String.
Dim tb As New TextBox
tb.Text = "my string"
i = tb.Text.IndexOf("string")

'Here is a LastIndexOf example for you:
Dim strFilePath As String = "C:\Temp\MyFile.txt"
Dim i As Integer
i = strFilePath.LastIndexOf("\")
     ' i now equals the integer 7:  the exact position of the last "\" (see notes below).

** Only 2 points to be aware of as you start using IndexOf and LastIndexOf:
1.  If no match is found, then a -1 is returned, not a 0 as with the Instr and InstrRev functions.
          'Here, a -1 will be returned, because the question mark is not found.
          i = "My String".IndexOf("?")

2.  Strings are zero (0) based in .NET.
          'So for example, the integer "3" will be returned,
          '      because the first character in the string "M" is position 0.
          i = "My String".IndexOf("String")

One final note:
'If you want to search for an exact match, then use the default,
i = "My String".IndexOf("String")

'However, if you want to search for a string, but you want to ignore the case
'such as UPPER CASE, Mixed Case, and lower case, then make sure you use the following:
i = "My String".IndexOf("string", StringComparison.CurrentCultureIgnoreCase)

So, in summary:
-  If you used the Instr method in VB6, use the IndexOf method in .NET.
-  If you used the InstrRev method in VB6, use the LastIndexOf method in .NET.

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Expert Comment

by:Jeff Certain
Comment Utility
To elaborate on what VBRocks said, there is an entire library for VB6 compatibility. You just need to import Microsoft.VisualBasic to get Left, Right, Mid, and the rest of the string functions.

However, this namespace does not include DAO, ADO or RDO (the old VB6 data approaches). You'll either need to bring those in as their own libraries, or move to ADO .NET. Neither of these options is painless.

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